To catalyze DNA synthesis, retroviral reverse transcriptase requires a primer strand to extend and a template strand to copy. For HIV-1, the primer is the 3'-end of a partially unwound lysine(3) tRNA annealed to the PBS (primer binding site) 179 bases from the 5' end of the retroviral genomic RNA (Isel et al. 1995). Reverse transcription of the viral genomic RNA proceeds from the bound tRNA primer to the 5' end of the viral RNA, yielding a minus-strand strong-stop DNA (-sssDNA) complementary to the R and U5 elements of the HIV-1 viral genome, as shown in the figure below (Telesnitsky and Goff 1997; Jonckheere et al. 2000). The reaction takes place in the host cell cytosol, and is catalyzed by the reverse transcriptase activity of the HIV-1 RT heterodimer.
NucleoCapsid (NC) protein prevents self-priming by generating or stabilizing a thermodynamically favored RNA-DNA heteroduplex instead of the kinetically favored TAR hairpin seen in reverse transcription experiments in vitro (Driscoll and Hughes 2000).